In discontinuous filter presses of this type the liquid portion of the material to be pressed is let off to the outside via filters by means of the action of a compressing pressure. In the process the compressing pressure is applied directly to the material to be pressed via a rigid pressure plate or pneumatically or hydraulically via a flexible diaphragm. The question arises at the start of feeding-in the material to be pressed as to what amounts must be fed into the pressing chamber so that there is a press pad sufficient for a first pressing. It should be noted in this connection that in the extended position of the pressure plate or the diaphragm the ratio between the effective filter surface and the instantaneous pressing chamber volume is greater than with the pressing element retracted.
The question arises in connection with the subsequent further fill process as to what amounts should be refilled per stroke of the pressing element so that an advantageous juice extraction behavior is achieved. Different problems arise with organic and inorganic materials regarding the material to be pressed. In connection with organic materials it is typical that the processability in the press (compressibility) greatly changes from batch to batch. Accordingly, a known continuous adaptation of the process parameters by hand assumes great experience and continued monitoring of the press during the filling operation by the operators.
Known attempts to automate required adaptations of the process parameters have remained without results. A usable understanding of the processes during the pressing operation by means of a model has not been successful so far.
Filling of the presses in particular makes very high demands on the operator. For example, the following set points must be predetermined in connection with a horizontal filter press for fruit material:
Total amount of the fill. This is greatly dependent on the compressibility of the material to be pressed. Hard to compress materials permit only small amounts of fill, while easily compressible materials permit large amounts of fill.
Amount of pre-fill. The same requirements apply here as with the total amount of fill. Too small or to large amounts of pre-fill have a very negative effect on the yield/output behavior.
Amount of fill per piston stroke. Following the end of pre-filling, a defined amount of material to be pressed is added per piston stroke in known pressing operations. These batch-wise filling pulses take place until the predetermined total amount of fill has been achieved as the sum. The appropriate selection of this amount of fill as a process value also very heavily depends on the compressibility of the material.
The result as a whole is that the pressing results are very different, depending on the ability and experience of the operator since, because of the required guesses, manual predeterminations of the process parameters very seldom result in an optimal yield/output behavior of the pressing operations.